In order to gain a better understanding of the neurobiology of positive feedback on gonadotropin secretion we are studying the hormonal regulation of neurotransmitter expression in the anteroventral periventricular nucleus of the preoptic region (AVPV) of juvenile female rats. The AVPV is a sexually dimorphic nucleus that plays an essential role in regulating preovulatory surges of luteinizing hormone (LH) and prolactin secretion and contains sexually dimorphic populations of neurotransmitter specific neurons that are regulated differentially by estrogen (E2) and progesterone (P4). Glutamate is an important regulator of GnRH secretion during pubertal development, but its sites of action remain largely unknown. Progress during the last year includes a study that showed that NMDA (R1) receptor gene expression is induced by E2 in the ventral part of the lateral septum, which provides a direct input to the AVPV. In addition, we used histochemical methods to demonstrate that neurons in the AVPV express both NMDA (RI) and AMPA (GluR1, GluR2, and GluR3, but not GluR4-7) glutamate receptor subtypes. Treatment of ovariectomized juvenile rats with exogenous estradiol caused a significant increase in the ratio of GluR1/GluR2. However, neither levels of GluR3 mRNA, nor the GluR3/GluR2 ratio, were altered significantly by estrogen treatment. These findings suggest that estrogen may facilitate Ca2+ influx in the AVPV by inducing the expression of GluR1 and we are currently using calcium imaging to test this hypothesis directly. Moreover, we have adapted this method for the study of primate prefrontal cortex in preparation for experiments that will examine the role of hormones in regulating glutamatergic signaling in the nonhuman primate brain.